HK1141582B - Vibratory flow meter and method for correcting for an entrained phase in a two-phase flow of a flow material - Google Patents

Description

Vibratory flowmeter and method for correcting entrained phase of a two-phase flow of a flow material

Technical Field

The present invention relates to a vibratory flow meter and method, and more particularly, to a vibratory flow meter and method for correcting for entrained phases in a two-phase flow of a flow material.

Background

Vibrating conduit sensors, such as Coriolis mass flowmeters and vibrating densitometers, typically operate by detecting motion of a vibrating conduit that includes a flow material. Properties related to the material in the pipe, such as mass flow, density, etc., may be determined by processing measurement signals received from motion sensors associated with the pipe. The vibration modes of a system filled with a vibrating material are generally affected by the combined mass, stiffness and damping characteristics of the containing conduit and the material contained therein.

A typical Coriolis mass flowmeter includes one or more conduits connected inline in a pipeline or other transport system and carrying materials such as fluids, slurries, emulsions, etc. in the system. Each conduit may be viewed as having a set of natural vibration modes including, for example, simple bending, torsional, radial, and coupled modes. In a typical Coriolis mass flow measurement application, a conduit is excited in one or more vibration modes as material flows through the conduit, and the motion of the conduit is measured at points spaced along the conduit. The excitation is typically provided by an actuator, for example an electromechanical device such as a voice coil type driver which perturbs the conduit in a periodic manner. The mass flow rate may be determined by measuring the time delay or phase difference between the movements at the sensor location. Two such sensors (or pickoff sensors) are typically employed to measure the vibrational response of the flow conduit(s), and are typically located at positions upstream and downstream of the actuator. The two pickoff sensors are connected to the electronics by a cable, such as by two pairs of independent wires. The instrument receives signals from the two pickoff sensors and processes the signals to derive a mass flow rate measurement.

Flow meters are used to perform a wide variety of mass flow rate measurements of fluid flows. One area in which Coriolis flow meters may be used is in the metering of oil and gas wells. The products of such wells include multiphase streams comprising oil or gas, but also other components including, for example, water and air, and/or solids. It is highly desirable that even for such multiphase flows, the resulting metering be as accurate as possible.

Coriolis meters provide high precision for single phase flow. However, when a Coriolis flowmeter is used to measure (aerated fluid or fluid (emulsion)) including entrained gas, the accuracy of the meter may be significantly reduced. The same is true for entrained solids (slurry).

Entrained air is generally present as bubbles in the flowing material. The size of the bubbles may vary depending on the amount of air present, the pressure and temperature of the flowing material. The degree of performance degradation is not only related to how much gas is present in total, but also to the size of the individual bubbles in the stream. The size of the bubble affects the accuracy of the measurement.

One important error source is fluid decoupling (decouple). The fluid decoupling results from the movement of the bubble relative to the liquid due to the vibration of the tube. The relative motion of the bubbles with respect to the liquid is driven by a buoyancy force similar to the force that causes the bubbles to rise to the surface under the influence of gravity. However, in the vibrating tube, it is the acceleration of the vibrating tube rather than the gravitational acceleration that causes the bubble to move. Since dense fluid resists acceleration more strongly than light bubbles, the bubbles are accelerated in the same direction as the tube acceleration. The bubbles move faster and further than the flow tube and the bubble movement causes some fluid to flow slower than the flow tube. This is the basis of the decoupling problem. As a result, fluids with lower vibration amplitudes experience less Coriolis acceleration and impart less Coriolis force to the flow tube than in the absence of bubbles. This results in the flow rate and density characteristics being underestimated (negative flow and density errors) when entrained gas is present.

The slurry exhibits problems similar to decoupling. However, in the case of slurries, the solid particles are often heavier than the liquid. The heavier particles move less than the liquid under acceleration of the vibrating tube. This forces some of the liquid to move much more than the vibrating tube. The result is that the liquid is overestimated (positive flow and density error) when there are particles heavier than the liquid. In both cases, the differential motion of the entrained phase is driven by the density difference between the entrained phase and the liquid. If the compressibility of the gas is neglected, the same equation can be used to describe the behavior of both entrained air and particles. Subtracting the entrained phase density with the liquid density gives a positive number for gas and a negative number for solid. The decoupling of the slurry is only negative. For this reason, the term decoupling will be used interchangeably for both emulsions and slurries.

Compensating for fluid decoupling has been difficult because there are several factors that determine how much the bubble moves relative to the liquid. Fluid viscosity is a significant factor. In very viscous fluids, bubbles (or particles) are effectively fixed in the fluid with little flow error.

Another effect on bubble mobility is bubble size. The drag on the bubble is proportional to the surface area, while the buoyancy is proportional to the volume. Thus, very small bubbles have a high resistance-to-buoyancy ratio and tend to move with the fluid. Small bubbles therefore cause small errors. In contrast, large bubbles do not tend to move with the fluid and cause large errors. This also applies to the particles. Small particles tend to move with the fluid and cause small errors.

The density difference between the fluid and the gas is another factor. Buoyancy is proportional to the difference in density between the fluid and the gas. The high pressure gas can have a density high enough to affect buoyancy and reduce decoupling effects. In addition, large bubbles occupy a larger volume, resulting in true fluctuations in the density of the flowing material. Due to the compressibility of the gas, the bubbles may vary in gas quantity, not necessarily in size. Conversely, if the pressure changes, the bubble size can change accordingly, expanding as the pressure decreases or contracting as the pressure increases. This may also cause a change in the natural or resonant frequency of the flow meter and thus a change in the actual two-phase density.

Second order factors may also have an effect on bubble and particle mobility. Turbulence in high flow rate fluids breaks large bubbles and particles small, thus reducing decoupling errors. The surfactant reduces the surface tension of the bubbles and reduces their tendency to polymerize. The valve can reduce the bubble size by increased turbulence, while the line bend can increase the bubble size by forcing the bubbles together by means of centrifugal forces.

There remains a need in the art for a vibratory flow meter that detects problematic levels of entrained second phase material. There remains a need in the art for a vibratory flow meter that is capable of accurately measuring flow characteristics in the presence of entrained second phase material. There remains a need in the art for a vibratory flow meter that can accurately measure flow characteristics at different levels of entrained second phase material.

Disclosure of Invention

A vibratory flowmeter for correcting for entrained phases in a two-phase flow of a flow material is provided according to an embodiment of the invention. The vibratory flow meter includes a flow meter assembly including a driver, and the vibratory flow meter is configured to generate a vibrational response to a flow material. The vibratory flow meter further includes meter electronics coupled to the flow meter assembly and receiving the vibrational response. The meter electronics is configured to determine a two-phase density of the measured two-phase flow using the vibrational response, determine a calculated drive power consumed by a driver of the flowmeter assembly, and calculate a density compensation factor using a liquid density of a liquid component of the two-phase flow, an entrained phase density of the entrained component, the measured two-phase density, and the calculated drive power.

A method of correcting for entrained phase in a two-phase flow of a flow material in a vibratory flowmeter is provided according to an embodiment of the invention. The method includes generating a measured two-phase density of the two-phase flow, determining a calculated drive power consumed by a driver of the vibratory flowmeter, and calculating a density compensation factor using a liquid density of a liquid component of the two-phase flow, an entrained phase density of an entrained component, the measured two-phase density, and the calculated drive power.

A method of correcting for entrained phase in a two-phase flow of a flow material in a vibratory flowmeter is provided according to an embodiment of the invention. The method includes generating a measured two-phase density of the two-phase flow, determining a calculated drive power consumed by a driver of the vibratory flowmeter, calculating a density compensation factor using a liquid density of a liquid component of the two-phase flow, an entrained phase density of the entrained component, the measured two-phase density, and the calculated drive power, and adding the density compensation factor to the measured two-phase density to provide a compensated two-phase density. The method also includes determining a predicted drive power using the density of the liquid, the density of the entrained phase of the entrained component, the density of the compensated two-phase, and a power characteristic of the vibratory flow meter. The method also includes determining an accuracy of a flow measurement of the vibratory flowmeter based on a difference between the predicted drive power value and the calculated drive power.

Aspects of the invention

In one aspect of the vibratory flow meter, the meter electronics is configured to multiply the drive voltage with the drive current to determine a calculated drive power.

In another aspect of the vibratory flow meter, the meter electronics is configured to multiply the pickoff sensor voltage with the drive current to determine a calculated drive power.

In yet another aspect of the vibratory flow meter, the meter electronics are configured as peer-to-peerSolving to determine a calculated drive power, where K is a proportionality constant, I_dIs a measured drive current, I₀Is a zero volume fraction drive current, E_POIs a pickup voltage, and E_tIs the pickup target voltage.

In yet another aspect of the vibratory flowmeter, calculating the density compensation factor comprises equatingSolving where (p)_l) Is the liquid density (p)_uut) Is an index density (p)_e) Is the density of the entrained phase (p)_computed) Is to calculate the driving power, and items C1 and C2 include predetermined instrumentsTable specific constants.

In yet another aspect of the vibratory flow meter, the meter electronics are further configured to add a density compensation factor to the measured two-phase density to provide a compensated two-phase density.

In yet another aspect of the vibratory flow meter, the meter electronics are further configured to add a density compensation factor to the measured two-phase density to provide a compensated two-phase density, determine a predicted drive power using the liquid density, the entrained phase density, the compensated two-phase density, and a power characteristic of the vibratory flow meter, and determine an accuracy of a flow measurement of the vibratory flow meter based on a difference between the predicted drive power value and the calculated drive power.

In yet another aspect of the vibratory flow meter, the meter electronics are further configured to be peer-to-peerSolving to obtain a compensated volume fraction of the two-phase flow, where ρ_compIs to compensate for the two-phase density.

In yet another aspect of the vibratory flow meter, determining the accuracy further comprises generating an alarm indication if the calculated drive power differs from the predicted drive power by more than a predetermined tolerance.

In yet another aspect of the vibratory flow meter, determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive entrained phase level and further indicating a change in a desired flow condition in the vibratory flow meter.

In yet another aspect of the vibratory flow meter, determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive bubble size and further indicating a change in a desired flow condition in the vibratory flow meter.

In yet another aspect of the vibratory flow meter, determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive solids entrained phase level and further indicating a change in a desired flow condition in the vibratory flow meter.

In yet another aspect of the vibratory flow meter, determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold.

In yet another aspect of the vibratory flow meter, determining the accuracy further comprises refining the compensated two-phase density if the calculated drive power is less than the predicted drive power and exceeds a predetermined lower threshold, or if the calculated drive power is greater than the predicted drive power and exceeds a predetermined upper threshold.

In yet another aspect of the vibratory flow meter, refining the compensated two-phase density includes decreasing a density compensation factor by an amount proportional to a difference between the calculated drive power and the predetermined lower threshold.

In yet another aspect of the vibratory flow meter, determining the accuracy further comprises comparing the predicted drive power to the calculated drive power, generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold, and refining the compensated two-phase density by reducing the density compensation factor by an amount proportional to a difference between the calculated drive power and the predetermined lower threshold if the calculated drive power is less than the predicted drive power, exceeding a predetermined lower threshold.

In one aspect of the method, determining the calculated drive power includes multiplying the drive voltage by the drive current.

In another aspect of the method, determining the calculated drive power includes multiplying the pickoff sensor voltage by the drive current.

In yet another aspect of the method, determining the calculated drive power includes peer-to-peerSolving, where K is a proportionality constant, I_dIs a measured drive current, I₀Is a zero volume fraction drive current, E_POIs a pickup voltage, and E_tIs the pickup target voltage.

In yet another aspect of the method, calculating the density compensation factor includes a peer-to-peer equationSolving where (p)_l) Is the liquid density (p)_uut) Is an index density (p)_computed) Is to calculate the driving power (p)_e) Is the entrained phase density, and the C1 and C2 terms include predetermined meter-specific constants.

In yet another aspect of the method, the method further comprises adding a density compensation factor to the measured two-phase density to provide a compensated two-phase density.

In yet another aspect of the method, the method further includes adding a density compensation factor to the measured two-phase density to provide a compensated two-phase density, determining a predicted drive power using the liquid density, the entrained phase density, the compensated two-phase density, and a power characteristic of the vibratory flow meter, and determining an accuracy of a flow measurement of the vibratory flow meter based on a difference between the predicted drive power value and the calculated drive power.

In yet another aspect of the method, the method further comprises peer-to-peerSolving to obtain a compensated volume fraction of the two-phase flow, wherein (ρ)_comp) Is to compensate for the two-phase density.

In yet another aspect of the method, determining the accuracy further comprises generating an alarm indication if the calculated drive power differs from the predicted drive power by more than a predetermined tolerance.

In yet another aspect of the method, determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive entrained phase level and further indicating a change in a desired flow condition in the vibratory flow meter.

In yet another aspect of the method, determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive bubble size and further indicating a change in a desired flow condition in the vibratory flow meter.

In yet another aspect of the method, determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive entrained solids level and further indicating a change in a desired flow condition in the vibratory flow meter.

In yet another aspect of the method, determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold.

In yet another aspect of the method, determining the accuracy further comprises refining the compensated two-phase density if the calculated drive power is less than the predicted drive power, exceeds a predetermined lower threshold, or if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold.

In yet another aspect of the method, refining the compensated two-phase density includes reducing a density compensation factor by an amount proportional to a difference between the calculated drive power and the predetermined lower threshold.

In yet another aspect of the method, determining the accuracy further comprises comparing the predicted drive power to the calculated drive power, generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold, and refining the compensated two-phase density by reducing the density compensation factor by an amount proportional to a difference between the calculated drive power and a predetermined lower threshold if the calculated drive power is less than the predicted drive power, exceeding a predetermined lower threshold.

Drawings

Fig. 1 illustrates a vibratory flowmeter for correcting for entrained phases in a two-phase flow of a flow material according to an embodiment of the invention.

Fig. 2 shows meter electronics of a vibratory flow meter according to an embodiment of the invention.

Fig. 3 is a flow diagram of a method for correcting entrained phase of a two-phase flow of a flow material in a vibratory flowmeter according to an embodiment of the invention.

Fig. 4 is a flow diagram of a method for correcting entrained phase of a two-phase flow of a flow material in a vibratory flowmeter according to an embodiment of the invention.

FIG. 5 is a graph of drive power versus gas volume fraction over a range of volume fractions for a plurality of fluid parameters that has been experimentally determined.

FIG. 6 is a graph showing calculated and predicted drive powers versus volume fraction of entrained phase.

Fig. 7 is a graph of calculated drive power and predicted drive power similar to fig. 6, except that the calculated drive power is shown to be less than the predicted drive power.

Detailed Description

Fig. 1-7 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. Certain conventional aspects have been simplified or omitted for purposes of teaching the principles of the invention. Those skilled in the art will recognize by way of these examples that variations are within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

Fig. 1 illustrates a vibratory flowmeter 5 for correcting for entrained phases in a two-phase flow of a fluid material according to an embodiment of the invention. The entrained phase may comprise entrained gas. The entrained phase may comprise entrained solids. The following discussion focuses on entrained gases. However, the discussion also applies to entrained solids.

The vibratory flow meter 5 includes a flow meter assembly 10 and meter electronics 20. The meter electronics 20 is connected to the meter assembly 10 via leads 100 and is configured to provide measurements of one or more of density, mass flow rate, volumetric flow rate, cumulative mass flow, temperature and other information over the communication path 26. It should be apparent to those skilled in the art that the present invention may be used in any type of Coriolis flowmeter, regardless of the number of operating modes of the driver, pickoff sensors, flow conduit, or vibration. Additionally, it should be appreciated that the vibratory flowmeter 5 can alternatively comprise a vibratory densitometer.

The flow meter assembly 10 includes a pair of flanges 101 and 101 ', manifolds 102 and 102 ', a driver 104, pickoff sensors 105 and 105 ', and flow conduits 103A and 103B. The driver 104 and pickoff sensors 105 and 105' are connected to the flow conduits 103A and 103B.

Flanges 101 and 101 'are attached to manifolds 102 and 102'. Manifolds 102 and 102' can be attached to opposite ends of spacer 106. Spacers 106 maintain spacing between manifolds 102 and 102' to prevent line forces from being transmitted to flow conduits 103A and 103B. When the flow meter assembly 10 is inserted into a pipeline (not shown) carrying the flow material being measured, the flow material enters the flow meter assembly 10 through the flange 101, passes through the inlet manifold 102 (where the total amount of flow material is directed into the flow conduits 103A and 103B), flows through the flow conduits 103A and 103B and exits the outlet manifold 102 ', where it exits the meter assembly 10 through the flange 101'.

Flow conduits 103A and 103B are selected and appropriately mounted to inlet and outlet manifolds 102 and 102 ' so as to have substantially the same mass distribution, moment of inertia, and elastic modulus about the bend axes W-W and W ' -W ', respectively. Flow conduits 103A and 103B extend outwardly from multiple branches 102 and 102' in a substantially parallel manner.

The flow conduits 103A and 103B are driven by the driver 104 in opposite directions about the respective bending axes W and W' and in a so-called first out-of-phase bending mode of the vibratory flow meter 5. The driver 104 may comprise one of a number of well-known arrangements, such as a magnet mounted to the flow conduit 103A and a reverse coil mounted to the flow conduit 103B. Alternating current passes through the opposing coils causing the two conduits to vibrate. An appropriate drive signal is applied by the meter electronics 20 to the driver 104 via lead 110.

The meter electronics 20 receives the sensor signals on leads 111 and 1111, respectively. The meter electronics 20 generates a drive signal on lead 110 that causes the driver 14 to oscillate the flow conduits 103A and 103B. Meter electronics 20 processes the left and right velocity signals from pickoff sensors 105 and 105' to calculate mass flow velocity. The communication path 26 provides input and output devices that allow the meter electronics 20 to interface with an operator or with other electronic systems. The description of FIG. 1 is provided merely as an example of the operation of a Coriolis flowmeter and is not intended to limit the teachings of the present invention.

The flow meter assembly 10 is configured to generate a vibrational response of the flow material. The meter electronics 20 may be configured to receive and process the vibrational response to generate one or more flow measurements of the flow material comprising the two-phase flow. The two-phase flow may include entrained gas (including entrained air) or entrained solids. The vibratory flow meter 5 is configured to correct for entrained gas and solids to produce a reliable and accurate flow measurement despite the entrained phase. In certain embodiments, the meter electronics 20 may receive and process the vibrational response to generate an alarm if the entrained phase level in the flow meter assembly 10 exceeds a predetermined level threshold (see fig. 4 and accompanying discussion). The alarm may indicate an excessive entrained phase level. The alarm may indicate excessive bubble size, such as if the bubble size exceeds a predetermined size threshold or gas volume. The alarm may indicate excessive particle size or solid volume. The alarm may thus indicate that the one or more flow measurements have exceeded a predetermined measurement tolerance. In certain embodiments, the meter electronics 20 may refine the correction if the resulting flow measurement is not accurate enough.

One common problem when generating the one or more flow measurements is when entrained air (or any gas) is present in the flow material. The entrained air may be present as bubbles of various sizes. When the bubbles are relatively small, they have negligible effect on the flow measurement. However, as the bubble size increases, the flow measurement error also increases.

Meter electronics 20 according to certain embodiments of the present invention produce improved flow measurements. The flow measurement is improved in the presence of entrained phases in the flow material. This flow measurement is improved in the presence of entrained air bubbles in the flowing material. The flow measurement is improved in the presence of entrained solids in the flow material. For example, the meter electronics 20 may produce an improved density measurement of the flowing material. The meter electronics 20 can additionally provide entrained volume fraction of the flowing material and/or other flow rate measurements. As a result, the vibratory flowmeter 5 can include a vibratory densitometer and/or a Coriolis flowmeter. Other additional flow measurements may be made and are within the scope of the description and claims.

In one embodiment, as shown, flow tubes 103A and 103B comprise substantially U-shaped flow tubes. Alternatively, in other embodiments, the flow tube may comprise a substantially straight flow tube. However, other shapes may also be used and are within the scope of the description and claims.

In one embodiment meter electronics 20 is configured to vibrate flow tubes 103A and 103B. The vibration is performed by the driver 104. The meter electronics 20 also receives the generated vibration signals from the pickoff sensors 105 and 105'. The vibration signal includes the vibrational response of the flow tubes 103A and 103B. The meter electronics 20 processes the vibrational response and determines the one or more flow measurements.

Fig. 2 shows meter electronics 20 of the vibratory flow meter 5 according to an embodiment of the invention. Meter electronics 20 includes an interface 201 that may be coupled to lead 100 (and optionally to communication path 26) in this embodiment. The meter electronics 20 also includes a processing system 203. The processing system 203 may comprise any manner of processing system including general or special purpose processors, circuits, and the like. The processing system 203 receives signals from the flow meter assembly 10 and processes the signals, such as vibrational responses from the pickoff sensors 105 and 105'. The processing system 203 can also generate and transmit signals to the flow meter assembly 10, such as drive signals that supply power to the driver 104.

The meter electronics 20 also includes a storage system 204 that stores information. The storage system 204 may be integrated into or separate from the processing system 203. For example, the storage system 204 may store the vibrational response 211, the measured two-phase density 212, the liquid density 2132, the calculated drive power 214, the density compensation factor 215, the compensated two-phase density 216, the predicted drive power 217, and the entrained phase density 218. Other information may be stored in the storage system 204, including the values discussed below.

The vibrational response 211 can include a vibrational response of the flow meter assembly 10. The vibrational response 211 comprises a pickup signal that has been processed to obtain a flow measurement. The vibrational response 211 can thus include flow measurements, including one or more of mass flow rate and volumetric flow rate. The flow rate may be stored as part of the vibrational response 211 or may be stored at a separate value.

Measuring the two-phase density 212 includes density measurements obtained from the pickoff sensors 105 and 105'. Measuring the two-phase density 212 includes generating a density measurement of the two-phase flow in the flow meter assembly 10 as is known in the art. As a result, the accuracy of the measured two-phase density 212 decreases as the amount of entrained air in the two-phase flow increases.

The liquid density 213 comprises a known density of the liquid component of the two-phase flow. The liquid density 213 may include a stored value or constant based on the liquid composition.

The entrained phase density 218 includes a known density (ρ) of an entrained second phase component of the two-phase flow_e). The entrained phase density 218 may include a stored value or constant based on the entrained component.

The calculated drive power 214 includes the electrical power required by the driver 104. Depending on the amount of entrained air, the driver 104 may or may not receive all of the required electrical power. The calculated drive power 214 may include calculations or measurements stored by the processing system 203. Calculating drive power 214 may include a drive current multiplied by a drive voltage (i.e., a current through driver 104 multiplied by a voltage at the driver). Alternatively, where the voltage at the driver 104 is not measured or otherwise known, calculating the drive power 214 may include a drive current multiplied by a pickup voltage at one of the pickup sensors. However, this approach also has disadvantages in that the drive current is generally not infinite and may not increase beyond a certain level, if at all possible. Accordingly, the calculated drive power 214 may be calculated from other values (see step 302 of FIG. 3, below).

For example, the density compensation factor 215 includes a compensation factor that will compensate the measured two-phase density 212 for the effects of an entrained phase, such as entrained gas. However, the gas may be varied and the density compensation factor 215 may compensate for any gas or mixture of gases. The density compensation factor 215 accounts for the presence of entrained gas. The density compensation factor 215 accounts for various levels of entrained gas.

The compensated two-phase density 216 includes a density value of the two-phase flow. In certain embodiments, compensating the two-phase density 216 includes measuring the two-phase density 212 in combination with a density compensation factor 215.

The predicted drive power 217 includes the drive power expected to be absorbed by a compensated two-phase density having an average bubble size or other desired fluid parameter (such as average viscosity, liquid density, etc.). The predicted drive power 217 includes a drive power calculated using the compensated two-phase density 216.

In operation and according to one embodiment, the processing system 203 receives a vibrational response 211, generates a measured two-phase density 212 from the vibrational response, and corrects for entrained phase at least in terms of density (see FIGS. 3-4 and the accompanying discussion).

Fig. 3 is a flow diagram 300 of a method for correcting entrained phase in a two-phase flow of a flow material in a vibratory flowmeter according to an embodiment of the invention. In step 301, the vibratory flow meter measures the density of the two-phase flow to obtain a measured two-phase density. As discussed previously, measuring the density of the two phases may have various degrees of error depending on the entrained phase level, flow rate, and other parameters of the flowing material.

In step 302, a calculated drive power is determined. The calculated drive power is the electrical power required by the driver of the vibratory flow meter to vibrate the flow conduit. The calculated drive power may be determined in one embodiment by multiplying the drive current by the drive voltage. Alternatively, the calculated drive power may be determined by multiplying the drive current by the pickup voltage present at one of the pickup sensors. The pickoff sensor voltage may comprise an acceptable substitute for the drive voltage, since the drive voltage is not typically measured or determined in a vibratory flow meter, while the pickoff sensor voltage is measured and known.

However, the power required to drive the flow conduit is proportional to the square of the vibration amplitude. Thus, when the target amplitude is doubled, the power required to reach the target vibration amplitude is quadrupled. Unfortunately, the drive current (I)_d) The current capability of the associated power source will not be exceeded and the driver may not necessarily receive the required drive current level in order to properly drive the flow conduit, particularly when there is a large entrained phase level in the two-phase flow. Thus, calculating the drive power may include the power required by the driver to fully vibrate the flow conduit, rather than the power consumed by the driver. Thus, the driver may require more power than supplied.

The calculated drive power calculated according to the present embodiment includes the power required to fully vibrate the flow pipe even when the available current is insufficient. The calculated driving power is calculated according to the following equation.

Wherein the term (K) is the proportionality constant of the vibratory flowmeter and the term (I)_d) Term is measurement of drive current, (I)₀) Term is zero volume fraction of drive current (such as calibration current), (E)_PO) Is a measured pickup voltage, and (E)_t) The term is the pickup target voltage. The solution of equation (1) determines the calculated drive power resulting from the presence of the entrained phase.

Item (I)_d×E_PO) Is a power term proportional to the total drive power consumed. Strictly speaking, the drive EMF voltage should be used instead of the pickup voltage (E)_PO) The driving power is calculated. However, the drive EMF is difficult to measure, while the pickup voltage (E) is easy to measure_PO) Proportional to the driving EMF. Thus, the pickup voltage (E) can be employed in the equation_PO). Pickup Voltage (E)_PO) And a drive current (I)_d) This product of (a) is proportional to the power required to vibrate the flow tube. Pickup target voltage (E)_t) Corresponding to a specified vibration amplitude target. Usually regulating the drive current (I)_d) To maintain the pickup voltage at its target voltage and thus the vibration amplitude at its target amplitude. However, entrained bubbles or entrained solids passing through the liquid exert a large damping force on the vibrating flow tube and are therefore often at the pickup voltage (E)_PO) Reaches its target voltage (E)_t) The drive current limit was previously reached. When this occurs, the voltage (E) is picked up_PO) Less than the target voltage (E)_t) And the vibration amplitude is smaller than its target.

Amplitude ratio termThe drive power is adjusted for the reduction in vibration amplitude due to the drive current reaching its limit. In other words, the power calculated in equation (1) is the power required to keep the vibration amplitude at its target even if this power is not available. When the vibration amplitude is at its target, then E_PO＝E_tAnd the voltage ratio term is equal to 1. Final term, I, in equation (1)₀×E_tThe term is the zero void fraction power required to drive the flow meter in the absence of a second phase (gas or solid). This term may include factory calibration power values. The zero void fraction power must be subtracted from the total power because pure liquid produces very little or no mass flow error. Equation (1) therefore calculates the power increase due to the entrained phase. This increase is roughly proportional to the error due to that phase. The zero volume fraction power may be determined during factory calibration.

In step 303, a density compensation factor is calculated. The density compensation factor may be calculated according to the following equation:

wherein (p)_uut) Phase is the uncorrected (i.e., measured or indicated) density of the meter, (ρ)_l) Is the known liquid density, (p)_computed) The phase is the drive power calculated according to equation (1). By uncorrected volume fractionTo correct the uncorrected density (p)_uut) Wherein (ρ)_e) Is the entrained phase density. For a particular flow meter type, the constants (C1) and (C2) may be determined for one flow meter type, which may be determined experimentally as C1-0.66 and C2-0.0015. However, it should be understood that these two constants may vary depending on the meter size, type, etc.

The density compensation equation (2) can be derived from the meter output parameters and the indicating/measuring volume fraction of the calculated drive power. It should be noted that the liquid density (ρ)_l) And entrained component density ρ_eMust be known in order to obtain an uncorrected volume fraction from the measured two-phase density. Note that if the entrained component is a gas at low pressure, its density may be approximately zeroThere is little or no degradation in the compensation. Note also that each instrument type may require a unique compensation equation.

In step 304, the density compensation factor is combined with the measured two-phase density of step 301 to obtain a compensated two-phase density (ρ)_comp). The compensated two-phase density more accurately reflects the density of the two-phase flow than the measured two-phase density. Compensating for the two-phase density minimizes the effect of entrained gas on the flow characteristic measurements. Compensating for the two-phase density minimizes the effect of larger bubbles on the flow characteristic measurement.

Fig. 4 is a flow diagram 400 of a method for correcting entrained phase of a two-phase flow of a flow material in a vibratory flowmeter according to an embodiment of the invention. At step 401, the vibratory flow meter measures the density of the two-phase flow to obtain a measured two-phase density, as previously discussed.

At step 402, a calculated drive power is determined, as previously discussed.

At step 403, density compensation factors are calculated, as previously discussed.

At step 404, the density compensation factor is combined with the measured two-phase density of step 401 to obtain a compensated two-phase density, as previously discussed.

In step 405, a predicted drive power is determined. The predicted drive power uses the compensated two-phase density to generate a drive power prediction. The predicted drive power (Y) may be generated using the compensated two-phase density according to the following equation:

wherein x is the compensating gas volume fractionρ_compIs a compensated density, and (p)_e) Is the entrained phase density.

FIG. 5 is a graph of drive power versus gas volume fraction over a range of volume fractions for a plurality of fluid parameters that has been determined experimentally. The graph reflects equation (3) above. The graph/equation may be used to derive the predicted drive power based on the compensation that has been performed. The lower line in the graph is the actual calculated drive power map for several smaller sized bubbles and the upper line is for several larger sized bubbles. It can be seen from the graph that larger bubbles require more drive power for the same void fraction of gas. It can also be seen from the graph that the characteristic power curve can be determined experimentally for a particular flow meter model. Using the gas volume fraction values generated by the previous density compensation process, the characteristic curves can be used to derive the predicted drive power.

Compensating for Volume Fraction (VF) by interpolation_compensated) The value (x term in the graph), the predicted drive power (Y term in the graph) can be obtained by equation (3). The compensating volume fraction may comprise a gas phase orVolume fraction of solid phase with respect to liquid phase. Compensated Volume Fraction (VF)_compensated) Is shown asTherefore, equation (3) uses the density compensation factor in the form of a compensated volume fraction to provide the predicted drive power (Y). In addition, the predicted drive power is derived using the power characteristics of the vibrating flow meter (constants C3 to C6). The power characteristic may be stored in the meter electronics or may be provided externally. The power characteristic may need to be derived independently for each vibratory flow meter model.

Referring again to fig. 4, in step 406, the predicted drive power is compared to the calculated drive power. This is done to determine the accuracy of the flow measurement. If the calculated drive power is within a predetermined tolerance of the predicted drive power, the flow measurement may be determined to be acceptably accurate. If not, an alarm indication may be generated.

Conditions of large entrained bubbles and low flow rates suffer from decoupling errors, as well as errors other than decoupling errors. This condition is called flow asymmetry and is the result of the response of the bubble to gravity. If the velocity of the gas bubbles rising relative to the fluid is comparable to the velocity of the fluid, the gas will slowly and accumulate in any down-flow tube region and quickly pass through any up-flow tube region. This asymmetry in gas distribution leads to atypical gas volume fractions in the meter and further causes excessive tube damping in the down-flowing flow tube region. As a result, the decoupled compensation under these conditions cannot be expected to eliminate flow and density errors and these conditions need to be identified for output warning or further compensation.

For very small bubbles and higher flow conditions, the flow asymmetry error is reduced because small bubbles tend to be carried by the fluid (high drag-buoyancy ratio). It is desirable to be able to identify such bubble types to compensate in different ways.

Similar flow asymmetry conditions exist for slurries. Large particles and low flow rates can cause particles to settle at low points in the meter. This causes atypical volume fractions of solids, excessive damping and uncompensated flow and density errors in the meter. This asymmetric condition also needs to be identified and a warning needs to be output.

In step 407, if the calculated drive power is within a predetermined tolerance amount of the predicted drive power, the compensated density measurement is considered accurate and compensated for. Otherwise, the flow measurement has become unacceptably inaccurate. Thus, the method continues to step 408.

In step 408, if the calculated drive power exceeds the predicted drive power by more than a predetermined upper threshold, the method branches to step 409. Otherwise, in case the calculated drive power is less than the predicted drive power, exceeding a predetermined lower threshold, the method branches to step 410.

FIG. 6 is a graph showing calculated and predicted drive powers versus volume fraction of entrained phase. In fig. 6, the calculated drive power is shown to be greater than the predicted drive power. The predicted drive power is the power required for nominal (nominal) entrained bubble size, fluid viscosity, and other parameters such as flow rate. The density compensation factor is also determined for the nominal fluid mixture parameter. Thus, if the calculated drive power is different from the predicted drive power, the compensated density is different from the true density of the two-phase mixture. For example, conditions such as large bubble size and low viscosity consume more power than predicted power and produce more error than the compensation factor correction. There is a correlation between power and density error because the same mechanism, fluid decoupling, that loses vibrational energy produces density error. Thus, the difference between the predicted power and the calculated power serves as a check to compensate for accuracy. In the present example, the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold (dashed line). Therefore, compensating density measurements may be considered to be unacceptably inaccurate. When this occurs, an alarm indicating a need to change the flow condition may be triggered, such as by mixing the flow or increasing the flow rate or pressure. Also, up to the upper threshold, the compensation coefficient equation may be changed for higher decoupling conditions.

Fig. 7 is a graph of calculated drive power and predicted drive power similar to fig. 6, except that the calculated drive power is shown to be less than the predicted drive power. This condition exists when the amount of fluid decoupling is less than the amount of fluid decoupling for the nominal condition used to determine the predicted power. In the present example, the calculated drive power is less than the predicted drive power, exceeding the predicted lower threshold (dashed line). Therefore, compensating the density of the two phases is not yet very precise. Thus, the compensation coefficient equation may be refined to reflect a lower amount of decoupling. The modified compensation coefficients produce a more accurate compensated two-phase density and cause the calculated drive power to more closely follow the predicted drive power.

Referring again to fig. 4, in step 409, if the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold, an alarm indication is generated. The alarm indication may be generated to alert an operator that an adverse flow condition is occurring. The alarm indication may be generated to alert that flow measurement has become unreliable. An alarm indication may be generated to warn of excessive entrained phase levels, such as excessive solids or excessive solid particle size, or excessive bubble size in the case of entrained gas. Additionally, an alarm indication may be generated to indicate a change in flow conditions. For example, the alarm indication may indicate a change in flow rate, flow pressure, or other flow condition. In certain embodiments, the alarm condition may be stored and/or transmitted, such as to an operator or technician who is able to change the flow condition.

At step 410, if the calculated drive power is less than the predicted drive power, the compensated two-phase density may be refined to improve accuracy and reliability of the flow measurement. In certain embodiments, the compensated two-phase density is refined by reducing the density compensation factor. In certain embodiments, the density compensation factor is reduced by an amount proportional to the difference between the calculated drive power and the predetermined lower threshold.

Claims (46)

1. A vibratory flowmeter (100) for correcting for entrained phases in a two-phase flow of a flow material, comprising a flowmeter assembly (10), the flowmeter assembly (10) comprising a driver (104), and wherein the vibratory flowmeter (100) is configured to generate a vibrational response for the flow material, and further comprising meter electronics (20) coupled to the flowmeter assembly (10) and receiving the vibrational response, wherein the vibratory flowmeter (100) is characterized by:

the meter electronics (20) is configured to generate a measured two-phase density of the two-phase flow using the vibrational response, determine a calculated drive power required by a driver (104) of the flowmeter assembly (10), and calculate a density compensation factor using a liquid density of a liquid component of the two-phase flow, an entrained phase density of the entrained component, the measured two-phase density, and the calculated drive power.

2. The vibratory flow meter (100) of claim 1, with the meter electronics (20) being configured to multiply the drive voltage with the drive current to determine the calculated drive power.

3. The vibratory flow meter (100) of claim 1, with the meter electronics (20) being configured to multiply the pickoff sensor voltage with the drive current to determine the calculated drive power.

4. The vibratory flow meter (100) of claim 1, with the meter electronics (20) being configured as a peer-to-peer equationSolving to determine the calculated drive power P_computedWherein K is a proportionality constant, I_dIs a measured drive current, I₀Is a zero volume fraction drive current, E_POIs a pickup voltage, and E_tIs the pickup target voltage.

5. The vibratory flow meter (100) of claim 4, with calculating the density compensation factor comprising pairingSolving, where p₁Is the liquid density, p_eIs the density of the entrained phase, p_uutIs a measure of the density of the two phases, P_computedIs to calculate the driving power, and wherein the C1 and C2 terms include predetermined meter-specific constants.

6. The vibratory flow meter (100) of claim 1, with the meter electronics (20) being further configured to combine the density compensation factor with the measured two-phase density to provide a compensated two-phase density.

7. The vibratory flow meter (100) of claim 1, with the meter electronics (20) being further configured to combine a density compensation factor with the measured two-phase density to provide a compensated two-phase density, determine a predicted drive power using the liquid density, the entrained phase density, the compensated two-phase density, and a power characteristic of the vibratory flow meter (100), and determine an accuracy of a flow measurement of the vibratory flow meter (100) based on a difference between the predicted drive power value and the calculated drive power.

8. The vibratory flow meter (100) of claim 7, with the meter electronics (20) being further configured to operate in accordance withTo obtain a compensated volume fraction VF, where p_compIs to compensate for the density of the two phases, p₁Is the liquid density, and p_eIs the entrained phase density.

9. The vibratory flow meter (100) of claim 7, with determining the accuracy further comprising generating an alarm indication if the calculated drive power differs from the predicted drive power by more than a predetermined tolerance.

10. The vibratory flow meter (100) of claim 7, with determining the accuracy further comprising generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive entrained phase level and further indicating a desired change in flow conditions in the vibratory flow meter.

11. The vibratory flow meter (100) of claim 7, with determining the accuracy further comprising generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive bubble size and further indicating a desired change in flow conditions in the vibratory flow meter.

12. The vibratory flow meter (100) of claim 7, with determining the accuracy further comprising generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive solids entrained phase level and further indicating a desired change in flow conditions in the vibratory flow meter.

13. The vibratory flow meter (100) of claim 7, with determining the accuracy further comprising generating an alarm indication if the calculated drive power is greater than the predicted drive power by more than a predetermined upper threshold.

14. The vibratory flow meter (100) of claim 7, with determining the accuracy further comprising refining the compensated two-phase density if the calculated drive power is less than the predicted drive power, exceeds a predetermined lower threshold, or if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold.

15. The vibratory flow meter (100) of claim 14, with refining the compensated two-phase density comprising reducing a density compensation factor by an amount proportional to a difference between the calculated drive power and the predetermined lower threshold.

16. The vibratory flow meter (100) of claim 7, with determining the accuracy further comprising comparing the predicted drive power to the calculated drive power, generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold, and refining the compensated two-phase density by reducing the density compensation factor by an amount proportional to a difference between the calculated drive power and the predetermined lower threshold if the calculated drive power is less than the predicted drive power, exceeding a predetermined lower threshold.

17. A method for correcting for an entrained phase in a two-phase flow of a flow material in a vibratory flowmeter, the method comprising generating a measured two-phase density of the two-phase flow, wherein the method is characterized by:

determining a calculated drive power required by a driver of the vibratory flow meter; and

the density compensation factor is calculated using the liquid density of the liquid component of the two-phase flow, the entrained phase density of the entrained component, the measured two-phase density, and the calculated drive power.

18. The method of claim 17, wherein determining the calculated drive power comprises multiplying the drive voltage by the drive current.

19. The method of claim 17, wherein determining a calculated drive power comprises multiplying a pickoff sensor voltage by a drive current.

20. The method of claim 17, wherein determining a calculated drive power comprises peer-to-peerSolving to determine the calculated drive power P_computedWherein K is a proportionality constant, I_dIs a measured drive current, I₀Is a zero volume fraction drive current, E_POIs a pickup voltage, and E_tIs the pickup target voltage.

21. The method of claim 20, wherein calculating a density compensation factor comprises pairingSolving, where p₁Is the liquid density, p_uutIs a measure of the density of the two phases, p_eIs the density of the entrained phase, P_computedIs to calculate the driving power, and wherein the C1 and C2 terms include predetermined meter-specific constants.

22. The method of claim 17, further comprising combining a density compensation factor with the measured two-phase density to provide a compensated two-phase density.

23. The method of claim 17, further comprising:

combining the density compensation factor with the measured two-phase density to provide a compensated two-phase density;

determining a predicted drive power using the liquid density, the entrained phase density, the compensated two-phase density, and a power characteristic of the vibratory flow meter; and

the accuracy of the flow measurement of the vibratory flowmeter is determined based on a difference between the predicted drive power value and the calculated drive power.

24. The method of claim 23, further comprising generating a signal based onTo obtain a compensated volume fraction VF, where p_compIs to compensate for the density of the two phases, p₁Is the liquid density, and p_eIs the entrained phase density.

25. The method of claim 23, wherein determining the accuracy further comprises generating an alarm indication if the calculated drive power differs from the predicted drive power by more than a predetermined tolerance.

26. The method of claim 23, wherein determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive entrained phase level and further indicating a desired change in flow conditions in the vibratory flow meter.

27. The method of claim 23, wherein determining accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive bubble size and further indicating a desired change in flow conditions in the vibratory flow meter.

28. The method of claim 23, wherein determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive solids entrained phase level and further indicating a desired change in flow conditions in the vibratory flow meter.

29. The method of claim 23, wherein determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power by more than a predetermined upper threshold.

30. The method of claim 23, wherein determining the accuracy further comprises refining the compensated two-phase density if the calculated drive power is less than the predicted drive power, exceeds a predetermined lower threshold, or if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold.

31. The method of claim 30, wherein refining the compensated two-phase density comprises reducing a density compensation factor by an amount proportional to a difference between the calculated drive power and the predetermined lower threshold.

32. The method of claim 23, wherein determining accuracy further comprises:

comparing the predicted drive power with the calculated drive power;

generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold; and

compensating for the two-phase density is refined by reducing the density compensation factor by an amount proportional to a difference between the calculated drive power and a predetermined lower threshold if the calculated drive power is less than the predicted drive power and exceeds the predetermined lower threshold.

33. A method for correcting for an entrained phase in a two-phase flow of a flow material in a vibratory flowmeter, the method comprising generating a measured two-phase density of the two-phase flow, wherein the method is characterized by:

determining a calculated drive power required by a driver of the vibratory flow meter;

calculating a density compensation factor using the liquid density of the liquid component of the two-phase flow, the entrained phase density of the entrained component, the measured two-phase density, and the calculated drive power;

combining the density compensation factor with the measured two-phase density to provide a compensated two-phase density;

determining a predicted drive power using the liquid density, the entrained phase density, the compensated two-phase density, and a power characteristic of the vibratory flow meter; and

the accuracy of the flow measurement of the vibratory flowmeter is determined based on a difference between the predicted drive power value and the calculated drive power.

34. The method of claim 33, wherein determining the calculated drive power comprises multiplying the drive voltage by the drive current.

35. The method of claim 33, wherein determining a calculated drive power comprises multiplying a pickoff sensor voltage by a drive current.

36. The method of claim 33, wherein the determiner is a determinerCalculating drive power includes peer-to-peerSolving to determine the calculated drive power P_computedWherein K is a proportionality constant, I_dIs a measured drive current, I₀Is a zero volume fraction drive current, E_POIs a pickup voltage, and E_tIs the pickup target voltage.

37. The method of claim 36, wherein calculating a density compensation factor comprises pairingSolving, where p₁Is the liquid density, p_eIs the density of the entrained phase, p_uutIs a measure of the density of the two phases, P_computedIs to calculate the driving power, and wherein the C1 and C2 terms include predetermined meter-specific constants.

38. The method of claim 33, further comprising generating a signal based onTo obtain a compensated volume fraction VF, where p_compIs to compensate for the density of the two phases, p₁Is the liquid density, and p_eIs the entrained phase density.

39. The method of claim 33, wherein determining the accuracy further comprises generating an alarm indication if the calculated drive power differs from the predicted drive power by more than a predetermined tolerance.

40. The method of claim 33, wherein determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive entrained phase level and further indicating a desired change in flow conditions in the vibratory flow meter.

41. The method of claim 33, wherein determining accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive bubble size and further indicating a desired change in flow conditions in the vibratory flow meter.

42. The method of claim 33, wherein determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold, indicating an excessive solids entrained phase level and further indicating a desired change in flow conditions in the vibratory flow meter.

43. The method of claim 33, wherein determining the accuracy further comprises generating an alarm indication if the calculated drive power is greater than the predicted drive power by more than a predetermined upper threshold.

44. The method of claim 33, wherein determining the accuracy further comprises refining the compensated two-phase density if the calculated drive power is less than the predicted drive power, exceeds a predetermined lower threshold, or if the calculated drive power is greater than the predicted drive power, exceeds a predetermined upper threshold.

45. The method of claim 44, wherein refining the compensated two-phase density comprises reducing a density compensation factor by an amount proportional to a difference between the calculated drive power and the predetermined lower threshold.

46. The method of claim 33, wherein determining accuracy further comprises:

comparing the predicted drive power with the calculated drive power;

generating an alarm indication if the calculated drive power is greater than the predicted drive power, exceeding a predetermined upper threshold; and

the compensated two-phase density is refined by reducing the density compensation factor by an amount proportional to the difference between the calculated drive power and a predetermined lower threshold if the calculated drive power is less than the predicted drive power, exceeding the predetermined lower threshold.